The present invention relates to liquid delivery devices, and particularly to devices for delivering liquids containing drugs. The drugs may be in solution and/or suspension in a pharmaceutically acceptable medium which is in the liquid state under normal temperature and pressure.
Our prior U.S. Pat. No. 5,062,834 discloses a liquid delivery device including an outer housing having an outlet for the liquid to be delivered, a displaceable member within the housing defining a first contractible chamber on one side of the displaceable member for holding a supply of the material to be delivered via the outlet, and a second contractible chamber on the opposite side of the displaceable member. The device further includes pressure-control means for controlling the pressure produced in the second contractible chamber for controlling the displacement of the displaceable member, and thereby the rate of flow of the liquid via the outlet. In the device described in that patent application, the pressure-control means comprised an electrolytic cell having a pair of electrodes separated by an electrolyte capable of generating a gas applied to the second chamber according to the electrical current passing through the electrolyte.
A drawback in the device described in that patent is that the rate of flow of the liquid (e.g., a drug) via the outlet is very sensitive to variations in ambient pressure and temperature, and/or to any leakage in the pressure control chamber.